Should I Close the Windows When Using a Dehumidifier?

The main purpose of a dehumidifier is to reduce humidity levels indoors. However, dehumidifiers can be quite expensive, from purchase to operation and maintenance. After all, to some extent, opening windows can achieve a similar dehumidifying result but only if the outdoor conditions are right. Simply opening windows isn’t always the solution. For one, the relative humidity outside may be even higher than the inside.

The most effective and efficient way to maintain humidity is still by using a dehumidifier. It allows you to control the exact humidity levels in your indoor space, preventing mold and musty odors. If you look at your dehumidifier manual, it usually has specific instructions to close the windows when running the dehumidifier. 

If the humidity outside is higher than the humidity inside, keeping your windows open introduces more air to dehumidify and the dehumidifier will keep running but never achieve your desired humidity level. Most people aim for 55-60% relative humidity indoors, so if you’re running a dehumidifier it’s better to keep the windows closed if the outside humidity is above this range.

Closing the Windows

Can You Open Windows When Using a Dehumidifier?

Sometimes you just need to open the windows even if the conditions aren’t ideal. Maybe you need to air out the room to get rid of a stale smell or just let an outdoor breeze in. So should you use a dehumidifier while the window or door is open?

Open Windows When Using a Dehumidifier

The short answer is no, you shouldn’t open windows with your dehumidifier running. A dehumidifier works best in a sealed space where it can keep cycling the same set of air in the room until it reaches the ideal target humidity. Opening windows introduces more moisture from the outside air if the air outside is humid. You’re essentially dehumidifying even the outside, increasing the area your dehumidifier needs to cover. 

Even a small crack allows moist air to seep inside, making the task tougher for your dehumidifier. This results in higher energy costs and inefficient dehumidification.

The one exception is if you’re in a dry climate, especially during the middle of the day when the sun is shining and outdoor humidity is low. Typically an ideal indoor humidity level for human health and comfort is around 55-60%. So if outdoor humidity is lower than 55-60%, opening the window could actually help your dehumidifier work faster and save some electricity.

If you want to dehumidify two adjacent rooms, it’s possible to use one dehumidifier and simply open a door between the two rooms given that you keep other doors and windows closed to the outside.

There are also cases when opening the window is better than running a dehumidifier, particularly when the humidity inside the room is higher than the relative humidity outside. For instance, after taking a hot shower, you should open a window or run an exhaust fan to keep the steam out. 

Other household activities such as washing dishes or hanging laundry can also temporarily add moisture to the air. In this case, you can simply open a window to air out the space and alleviate the humidity.

If you need to dehumidify multiple rooms at the same time, it may be a good idea to opt for a whole-house dehumidifier. With this type of dehumidifier, it can actually help to leave your interior doors open to even out the dry air in the space.

When to Use a Dehumidifier

If you have high humidity

The most obvious reason to use a dehumidifier is if the humidity is too high. Remember that the ideal indoor humidity is from 30% to 50% RH. It may be more convenient to use a hygrometer to measure the exact relative humidity in your home. If the device often reads 60% and above, this may be a sign that you need a dehumidifier for your home. 

Humidity can sneak in through the crevices of your home and you might not notice it until it has already caused severe damage. If you live in a high-humidity region or in a small apartment with poor ventilation, you can expect high humidity indoors when it’s also humid outside. If you don;t have a way to measure the exact humidity, watch out for some common signs of excess humidity inside the house. 

Control Humidity

If you have respiratory issues

Damp, dark, and cold areas become a breeding ground for mold, mildew, and bacteria. Mold can spread spores through the air and grow on any moist surface. Dust mites also thrive in humid environments. When inhaled, mold spores and dust mite waste materials can trigger allergic reactions, asthma attacks, and other respiratory conditions. So if you often suffer from these issues in your home, this may be the sign for you to use a dehumidifier to improve indoor air quality and relative humidity.

If there is mold and musty odors

Musty or moldy odors are another sure indicator of high relative humidity. Dark spots of greenish or black colors on the bathroom walls, under the sinks, or around the toilet and bathtub, are some of the most common types of mold in the house. Moist and porous materials such as wood and fabric are particularly vulnerable to mold growth. Once mold finds a moist surface to settle, it can quickly spread and feeds off of the material. If you notice a musty smell but can’t find the source, look behind furniture, under carpets, or more likely in the crawl space. 

If there is damage to your house structure

Damages start from seemingly harmless damp spots or condensation on windows and other cold surfaces, especially in the bathroom, basement, or kitchen. In worse cases, you may find water stains on the walls and ceiling, and eventually, mold growth. Too much moisture in the environment can cause wood to rot and metals to rust and corrode. If you see any of these signs, it can cause permanent damage to your house structure and other belongings if left unattended for much longer. 

If there is damage to your house structure

How Does a Dehumidifier Work?

The main purpose of a dehumidifier is to reduce relative humidity in an indoor space. It extracts excess moisture from the air using different methods. The two main types of dehumidifiers are called refrigerant and desiccant. 

The refrigerant dehumidifier works similarly to an air conditioner. It uses a compressor to pump the refrigerant through the cooling system. Warm, humid air is drawn by a fan then the air passes over the cold coils. As the air cools down, the vapor condenses into water droplets. This is what your dehumidifier collects in its water tank. Then, the drier air is released into the room.

On the other hand, a desiccant dehumidifier extracts moisture from the air it comes into contact with until the desiccant’s maximum extraction capacity is reached. Most desiccant dehumidifiers are either disposable or rechargeable. If the desiccant is renewable, such as silica gel, it can be reheated to dry out the moisture. This type is ideal in situations where the air temperature is lower than a refrigerant dehumidifier can handle.

Where to Place a Dehumidifier

Proper placement can make all the difference to your dehumidifier’s performance. When choosing the placement for your dehumidifier in any room, you must consider the following factors to maximize its efficiency. 

Humidity Source

To find the best place for your dehumidifier, the first thing you must know is the main source of moisture in the house. Any room can become humid depending on the climate, but some parts of the house are more prone to moisture than others. This includes the basement, crawl space, and bathroom. In some cases, a dehumidifier alone cannot solve your humidity problem if the source of moisture is always present. 

For example, if you have a bathroom where people are showering frequently, it can add humidity to its surrounding space. Basements are also commonly the most humid part of the house due to rain or groundwater that seeps into the soil. Most indoor humidity problems are related to the outdoor relative humidity. If the air is humid outside, chances are it’s also humid inside. Tiny cracks in your walls and foundations allow warm air to seep inside. Furthermore, improper installation of gutters and downspouts can cause rainwater to flow toward your foundation and into the basement.

If you have any of these problems, contact a licensed contractor to plan the best course of action. In any of these cases, it’s critical to track down the main source of humidity first before placing a dehumidifier in any of your rooms. 

Open Shower create humidity

Air Circulation 

No matter what room you place a dehumidifier, it’s important to maintain proper air circulation to help the unit function properly. Make sure that the airflow isn’t blocked from the intake and exhaust grilles. Close all doors and windows, clear the area from any obstruction, and avoid the room corners as much as possible. It is recommended to keep the dehumidifier at least a few inches away from walls, furniture, and other items to allow the air to flow freely and prevent overheating. You may also want to install a fan to help circulate the air in the room.

Electricity and Drainage 

Most dehumidifiers directly remove moisture from the air, resulting in condensate which is then stored in an internal reservoir or drained through a hose. However, a dehumidifier is an electrical appliance and it can be a safety hazard around water . To be safe, place the unit far enough from electrical outlets where you can still plug the cord directly into a wall socket.

Additionally, if you’re using the tank to collect the condensate, you may need to empty it at least once or twice a day. Remember not to let standing water inside the dehumidifier for longer than two days for risks of mold growth. You must place the unit where you can easily access the tank without the risk of spilling water while removing the tank or tripping whilst you carry the tank of water to the drain location.

On the other hand, if you’re using a drain hose, you need a drain lower than the dehumidifier’s location. You must place the dehumidifier as close to the drain as possible. If you’re using a pump to drain water out of a window or into a sink, take note of the maximum drain height where you can position the hose end. You may also want to keep your dehumidifier easily accessible for monitoring and regular cleaning.

How to Choose the Right Dehumidifier for Room Size

When choosing a dehumidifier for the room, it’s absolutely essential to get the correct size for maximum effectiveness and efficiency. Two important factors you must always consider are the dehumidifier’s moisture removal capacity and coverage area.

Dehumidifier Capacity

This is the maximum amount of moisture it can extract from the air in 24 hours, typically measured in pints per day for residential dehumidifiers. Standard dehumidifiers today have a capacity ranging from 20 to 50 pints per day based on the most recent DOE rating standards. The actual amount of moisture your dehumidifier can remove per day depends mainly on the total size and dampness levels of your space. A larger and more humid space requires a higher capacity. However, this doesn’t mean that the highest capacity is always the best. Use only the exact size or the next bigger capacity you need for your space to get the most out of your unit.

Coverage Area

The efficiency of the dehumidifier largely depends on the amount of space that it has to handle. You can expect a dehumidifier to finish its task more quickly in a smaller area than a larger one with a similar humidity level. To determine which dehumidifier capacity is best for you, measure the dimensions of the space you need to dehumidify and take note of the humidity levels inside the room. Higher capacity typically means larger coverage area compared to dehumidifiers within the same brand.


Finally, once you’ve chosen a dehumidifier for your space, make sure you understand how it works and how you can maximize its efficiency. When using your dehumidifier, opening windows to the outside is never a good idea. The only time you may want to open a door is if you’re dehumidifying more than one room simultaneously. In some cases, it may be more efficient to simply keep a window open to let cool air into the room. However, this can take a long time and does not allow for precise humidity control. Thus, when using your dehumidifier, follow the manufacturer guidelines including closing all the windows.

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